The present invention relates to a hydraulic drive comprising a hydraulic motor which includes a first hydraulic connector and a second hydraulic connector. Such a hydraulic motor converts hydraulic energy into mechanical energy and is driven in that a pressure difference is applied between the first hydraulic connector and the second hydraulic connector of the hydraulic motor, whereby hydraulic fluid flows through the hydraulic motor. The rotary movement generated by the hydraulic motor is then determined by the displacement volume of the hydraulic motor and by the quantity of the hydraulic fluid flowing through the hydraulic motor.
Previously, essentially the control in an open circuit and the control in a closed circuit have been known for the operation of hydraulic motors. In an open circuit, one of the two hydraulic connectors has pressure applied via a control valve, whereas the other connector is subject to return pressure. A directional valve is provided for directional changes which reverses the assignment of the two hydraulic connectors. In a closed hydraulic circuit, the two hydraulic connectors of the hydraulic motor are, in contrast, directly connected to the hydraulic connectors of a hydraulic pump which hereby directly determines the volume flow through the hydraulic motor.
The disadvantages of an open circuit are in this respect the complicated priority switching, the numerous valves and logic systems which are required for the control and the lack of a precise torque control. The disadvantages of a system having a closed circuit are in particular the high costs since here a separate hydraulic pump has to be provided for each hydraulic motor.